Behaviour of aroma compounds during the oral processing of wine: modulation by wine composition and human physiology

Abstract

The main aim of this Thesis has been to gain understanding in the behaviour of aroma compounds during the oral processing of wine and how this behaviour can be modulated by oral physiological factors, such as saliva composition (salivary proteins, enzymes, flow), intrinsic individual factors (age, gender) or by the wine matrix composition (phenolic compounds, ethanol). Results from in vivo assays performed in simulated consumption conditions confirmed that some wine matrix components, such as ethanol and polyphenols have a large effect on oral aroma release and persistence. Ethanol increases the persistence of most wine volatiles, but this effect is modulated by the action of polyphenols (procyanidins). The effect of polyphenols on oral aroma release also depends on their class. While phenolic acids enhance the release of some volatiles, (e.g. β-phenyl ethanol, linalool), flavonoids and specially procyanidins decreased oral aroma release, mostly of ester compounds. These changes have a sensory impact, reducing the intensity perceived of the aroma descriptors associated to these volatiles. Additionally, the use of ex vivo wine-saliva systems allowed us unrevealing some interactions among typical wine volatile compounds and oral components (buccal cells, saliva mucins, enzymes), in presence and absence of phenolic compounds. Moreover, results from this Thesis represent an original contribution to understand the metabolism of aroma compounds in the mouth. In this work, it has been proven the hydrolysis of carboxylic esters by saliva esterase enzymes, the specificity of these enzymes for smaller carboxylic esters and their inhibition by typical wine phenolic compounds at natural red wine concentrations. Additionally, it was confirmed the individual differences on esterase activity and its relevance under wine consumption conditions (11% ethanol, pH = 5). Moreover, the application of cutting edge analytical methodologies, such as untargeted SOOM-GC-ToF-MS allowed us to confirm the novo formation of volatiles in the mouth from the hydrolysis of aroma molecules (carboxylic acids), wine odourless precursors (lactones) or from transesterification reactions (carboxylic esters). Focusing in a large number of wine volatiles from many different chemical families this work, has also proven that both, the physicochemical characteristics of the odorant and the chemical structure, but also the involvement of oral physiology (metabolism by saliva enzymes, interaction with saliva proteins) determine the oral aroma persistence. Finally, this work also confirmed the higher differences in oral release behaviour depending on the age of the individuals. For instance, senior showed a higher intra-oral release of most volatiles compared to younger adults. On the contrary, the impact of the gender on aroma release was less noticeable. Overall, results from this work provides novel findings regarding the behaviour of aroma compounds in the mouth during wine tasting that is necessary to comprehensively explain wine aroma perception, contributing to better understand consumer’s behaviour and choice toward wine.